This invention relates to an improvement in a vane type hydraulic motor which comprises a rotor, a stator, vane slots in one of the rotor or stator, and vanes in the vane slots which sequentially traverse a high pressure zone, a transfer zone, a low pressure zone and a sealing zone when the motor is operating. More specifically, the invention relates to an improvement which maintains the vanes against the cam ring during the time the vanes traverse the transfer and sealing zones.
Conventional two-lip, solid vanes are well-known in the art and are commonly used in vane motors and pumps. As a vane traverses the transfer and sealing zones on the major and minor diameters respectively of the cam ring, one of the vane faces is exposed to high pressure fluid from the high pressure port while the other face is exposed to low pressure fluid from the low pressure port and the high pressure fluid tends to leak across one of the lips on the vane. This leakage creates a high pressure on top of the vane which tends to bias the vane inwardly of its vane slot and away from the cam ring. Separation of the vane from the cam ring is potentially disastrous, since it provides a short circuit path for high pressure fluid to reach the low pressure zone which is located in front of the vane when the device is acting as a motor.
In a vane motor springs positioned between the bottom of the vane slots and the bottom of the vanes are used to bias the vanes outwardly of the slots and against the cam ring. A problem with using springs to bias a solid vane is that if there is any leakage of high pressure fluid across the top of the vane a large force on top of the vane will result which will overcome the force of the springs and cause the vane to be moved inwardly of its slot away from the cam ring.
To overcome some of the problems associated with a solid two-lip vane, passages are formed in the vane, which passages connect the inner and outer ends of the vane. Such passages are shown in U.S. Pat. No. 3,359,914 to Adams, which is assigned to the assignee of the instant invention. The purpose of the passages as disclosed in the Adams' patent is to equalize or balance the pressure on the inner and outer ends of the vane at all times. Consequently, any fluid which leaks over a lip on the outer edge of the vane cannot cause a force buildup on the outer end of the vane since the inner and outer ends of the vane are connected.
An additional problem arises as a vane in pumps and motors traverses the transfer and sealing zones. In these zones one face of the vane is subjected to high pressure fluid, whereas the opposite face of the vane is exposed to low pressure fluid as mentioned above. The pressure differential which acts on opposite faces of the vane tends to move the vane sideways in its slot and hold it in one position in the slot due to friction. Consequently, if the cam ring moves away from the outer end of a vane a small amount due to manufacturing errors in the cam ring or due to flexure of the housing caused by pressure differences arising from the pumping action, a large force on the inner end of the vane is required to move the vane back into contact with the cam ring. Separation of a vane from the cam ring in the transfer and sealing zones is generally avoided in a vane pump by the use of a hydraulically operated piston which applies substantial pressure to the inner end of a vane in the transfer and sealing zones. The operation of a hydraulically operated piston can be seen in U.S. Pat. No. 3,223,044 which is assigned to the assignee of the instant invention. However, a hydraulic piston is generally not suitable for use in a vane motor. The reason is that in a motor the piston would be energized or biased upwardly in the major diameter portion of the cam ring which means the piston must travel a relatively long distance before it contacts the vane or before the vane contacts the cam ring which would cause excessive noise. In a pump the piston is energized in the minor diameter portion of the cam ring which means the piston travels a short distance before it contacts the vane and the noise is not excessive.
Separation of a vane from the cam ring in vane motors is due to the fact that springs are interposed between the bottom of the vane slot and the inner end of the vane to bias the vane outwardly of its slot into contact with the cam ring. However, due to size and space limitations the force of the springs is substantially less than the force of a hydraulically operated pin in a vane pump and the force of the springs is not sufficient to maintain the vane in contact with the cam ring as the vane traverses the transfer and sealing zones, particularly at low speeds. Consequently, the leakage rate of a vane motor is quite high and its efficiency is quite low.
It is desirable to provide a vane motor in which the vanes remain in contact with the cam ring as they traverse the transfer and sealing zones.
Also, it is desirable to provide a means for maintaining the vanes in contact with the cam ring which uses a minimum of force.
It is further desirable that the means for maintaining the vane in contact with the cam ring operates only in the areas of the transfer and sealing zones.
Moreover, it is desirable that the force exerted by the means for maintaining the vane in contact with the cam ring modulates in such a way that the force acting to bias the vane outwardly of the vane slots increases as the distance between the outer end of the vane and the cam ring increases.